This invention relates to pressure-sensitive adhesives. More particularly this invention relates to ultraviolet curable pressure-sensitive adhesives and methods for improving the coated state properties of these adhesives.
The use of ultraviolet curable pressure-sensitive adhesives is known. See, for example, an article by Dowbenko et al, entitled "Radiation Polymerization for Pressure-Sensitive Adhesives" in Chemtech, September 1974, p. 539. This article and patents, such as U.S. Pat. Nos. 3,424,638, 3,551,311, 3,328,194, and 3,725,115 disclose that many conventional ultraviolet systems may be made useful in pressure-sensitive applications by simply applying them to the desired substrate and curing by ultraviolet radiation. No substantial modification of traditional prior art ultraviolet curing technology is suggested in this article or in these patents.
However, prior art ultraviolet curable pressure-sensitive adhesives have been deficient in a number of properties, particularly adhesive and cohesive strengths.
Thus, it is an object of this invention to prepare pressure-sensitive adhesive systems curable by ultraviolet light, which systems have improved cohesive and adhesive strength.
It is another object of this invention to prepare ultraviolet curable pressure-sensitive adhesives having improved substrate adhesion.
These and other objectives are obtained by preparing the compositions according to the methods of the instant invention.